IMPLEMENTATION OF LEAN TECHNIQUE IN POLYMER MANUFACTURING

Concept :

Lean manufacturing is a systematic approach to identify and eliminate waste (non value-added activities) through continuous improvement by flowing the product at the pull of the customer in pursuit of perfection. Lean systems are highly flexible to customer requirements. Lean is all about doing more with less.It involves never ending efforts to eliminate or reduce muda (waste) in design, manufacturing, distribution and customer service process.

In this project, an attempt is made to investigate the current processes and scope of implementing lean manufacturing concepts in a polymer manufacturing industry located at Erode. Initially, visit to shop floor was made to study the various processes in the polymer manufacturing value chain. Value stream mapping (VSM) one of the lean tools is used to map the value stream of polymer manufacturing processes.

The different forms of value added and non-value added activities, and cycle times of process are identified in roll printing machine by using VSM. The scope of eliminating different forms of wastes using suitable lean tools such as SMED, 5S, POKA YOKE, KAIZEN etc. are studied.

In roll printing machine, it is required to change the set-ups due to variety of product changes. The set-up changes affect the productivity and results in non-value added activity. In order to bring the roll change to single minute, the “vacuum system” for paint spraying and “zero setting adjustment” for stereo pasting techniques are used  which decrease non value added time and increase productivity to bring the SMED technique effectively.

STATEMENT OF THE PROBLEM

Toyota production system is an automobile manufacturing industry and it is the first company to implement the lean concepts and its success is proven worldwide. Venbro polymer is a polymer manufacturing industry in which polymer bags are manufactured. Most of the issues in polymer manufacturing are originated due to uneven customer demand and more varieties. Hence it needs further investigation of manufacturing processes in polymer manufacturing and development of strategies to implement lean tools. Different types of machines are used to produce products at various stages of manufacturing. When the product variety changes, the machines are required to change the set-ups and other sub-assemblies to meet customer requirement. The set-up changes affect the productivity and results in non-value added activity. To eliminate the non-value added activity, it is proposed to use SMED principle (one of the lean tool) in this project.

METHODOLOGY

               As evidenced from the literature, the emphasis on promotion of lean concepts in polymer manufacturing industries is found to be inadequate. Hence, as a first step the awareness of lean practices and its implementation issues with specific reference to polymer industries in India are investigated. The methodology adapted to eliminate the non-value added activity is presented below.

PROCESS FLOW SEQUENCE

The above figure shows the process flow in Venbro polymer manufacturing industry. In tape plant, polypropylene and master batch are the raw materials and it’s mixed in a ratio of 75:25 by manually. The mixture is feed into the hopper and it flows to the oven and raw materials are heated at a temperature of 2500 C to convert from solid state to liquid state then passing fine sheet through roller.

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PROCESS FLOW SEQUENCE

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                  The above figure shows the process flow in Venbro polymer manufacturing industry. In tape plant, polypropylene and master batch are the raw materials and it’s mixed in a ratio of 75:25 by manually. The mixture is feed into the hopper and it flows to the oven and raw materials are heated at a temperature of 2500 C to convert from solid state to liquid state then passing fine sheet through roller.

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                  The fine sheets are to be cut by using thin blades and finally the hot tapes are to be cooled gradually and to be rolled in a bobbin. In loom section, the bobbin supplied from the tape plant are to be placed in wrap stand and it is to be weaved by horizontal and vertical supply of  yarn to produce  a polymer bag in a roll form. The polymer bag roll is passed to the lamination section. The polypropylene materials are used here for coating on the polymer bag roll to prevent the bags from moisture. The raw materials are feed into the hopper and it is to be heated at a temperature of 2500c. The heated materials are coated on the polymer bag rolls for lamination purpose. By laminating on the polymer bag rolls, it can increase the quality of the polymer bags. The laminated bags are conceded to the printing section.

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The stereos are pasted on the cylinder which is used to impress the product name on the polymer bags. When the stereos are impress against the polymer roll then the impression of the stereos are printed on the polymer roll. There are four dies are used in the Venbro polymer manufacturing industry, for single die time taken is about 25 minutes. Therefore, for changing four dies total time to be taken is about 1 hour. After printing is done on the polymer bags, it is to be moved to the cutting section.

In polymer manufacturing industry, they have an automatic cutting machine which is used to cut polymer bags. A programmable logic controller is attached for automation. An automated machine is performing tasks that are beyond human capabilities of size, weight, speed, endurance. The automatic cutting machine can be cut 35 polymer bags per minute depending upon their length. There is a sharp blade which is used to cut the polymer bags according to the required length. The blade is to be cut with the help of sensor. The sensor is a device which detects the state of the system. It senses the polymer bags when it reaches certain length, the blade is ready to cut the bags. The stitching is used to stitch the polymer bags on both side by using stitching machine and finally the stitched bag are packed by using hydraulic balling machine.

IDENTIFICATION OF VALUE STREAM AND VALUE

Value” is what the customer is buying. Value stream mapping is a Special type of flow chart that uses symbols known as “the language of Lean” to depict and improve the flow of inventory and information. VSM addresses material process sequences and flows as well as information flows that impact this movement. The purpose of value stream mapping is to Provide optimum value to the customer through a complete value creation process with minimum waste in design, build and sustain. It helps to understand and streamline work processes using the tools and techniques of Lean Manufacturing. It encourages data acquisition in a systematic manner that often gives additional insights.

Value stream mapping (VSM) is a lean tool that employs a flow diagram documenting in high detail every step of a process. Many lean practitioners see value stream mapping as the fundamental tool to identify waste, reduce process cycle times, and implement process improvement. A value stream map helps you quickly visualize your entire process, identifying bottlenecks or inefficiencies where the processes can be streamlined or improved. VSM should follow the some regulations which are given below.

  1. Identify the target product, product family, or service.
  2. Draw while on the shop floor a current state value stream map, which shows the current steps, delays, and information flows required to deliver the target product or service. This may be a production flow (raw materials to consumer) or a design flow (concept to launch). There are ‘standard’ symbols for representing supply chain entities.
  3. Assess the current state value stream map in terms of creating flow by eliminating waste.
  4. Draw a future state value stream map.
  5. Work toward the future state condition.

Value stream mapping can be classified into two types such as current state mapping and future state mapping. The current state mapping of conversion unit of polymer bags can be drawn by using  i-grapx.

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               The above figure shows the current state mapping of Venbro polymer manufacturing industry and the method that will be used in collecting data needed is observation to the activities that performed in the production shop floor. The operation process are involved in the manufacturing facility from raw materials to finished goods and  all the places where inventory is stored between the processes are identified, and observed how the material flows from one operation to another Statistical data collection methods for measuring machine setup time were used in this study to summaries and describe the data. Production process flow and standard operation procedure are reviewed briefly before setting up the data collection table is done. The data was collected by using a stopwatch. Based on the actual production, data was collected and recorded on a daily basis. These methods helps to identify the main contributor to high time loss and help to visualize and better understand the root causes and finding possible solutions to the problems. Implementation of SMED tool of this project is discussed in the next chapter.

ANALYZING SET-UP TIME

The first step in the analysis is to videotape every detail of the entire changeover process from cleanup to setup in the roll printing machine. The only exceptions are normal breaks such as lunch. It is important that the changeover being filmed is a normal changeover. If anything abnormal occurs, the changeover needs to be re-filmed.The next step is the process of stopping the machine. Each time it is necessary to make a changeover the machine must be stopped. After the machine is stopped, dismantling of old cylinder has to setup new cylinder. The stages of change over are sequenced below

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In a roll printing machine, the cylinder setups must have to change regularly due to variety of product changes. While the variety of product changes then the stereos, colour paint and cylinders are necessary to alteration. Some of the products are have to colour on both sides and it depends upon the customer requirements. Different size of cylinders is available. There is a stereo which is used to impression the desired matter against the polymer roll bags. The stereos are pasted on the cylinder approximately. After pasting stereo, the cylinder is to adjust for an exact arrangement. The current changeover of roll printing machine is shown in the figure below.

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After a first analysis it was possible to identify some problems that affected the quality and efficiency of the process. Thus, the main problems recorded were high setup times, large amounts of movements made by the operator and disorganization of equipment and materials.

 S. no.                     Task operation        Actual time
 

1.

 

Stereo pasting

 

4.30 min

 

2.

 

Colour changing

 

15.00 min

 

3.

 

Cylinder alignment

 

12.00 min

 

4.

 

Trail time

 

3.00 min

 

5.

 

Regular process starts

 

34.30 min

 

The above table shows the actual change over time practiced in the polymer industry. The operator takes more time for colour changing and cylinder alignment. There is a tray which is used to hold the colour paint and it applies to the cylinder for printing desired matter on the polymer roll bags. The tray is placed below the cylinder. When the product changes simultaneously the stereo and colour paint are also changes. By using thinner, the machinist cleans the colour paint which was in the tray. The total time taken for entire setup of roll printing machine is about 34.30 minutes. In order to reduce these non-value added time, two techniques are proposed such as “Vacuum pump system” and “Zero setting adjustment”. These proposals are designed by using creo-2 software version 2.0 and it is explained below

VACUUM PUMP SYSTEM

The time in cleaning and altering the colour paint is minimized by using vacuum pump system with nozzle instead of using manual cleaning and changing the colour paint. The proposed vacuum pump is shown in figure below

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The vacuum pump system is used to reduce the timing of cleaning and changing the colour paint. Its components are shown in the figure. The reservoir is used to store the colour paint and the pump is to suction the colour paint from the reservoir to the cylinder through nozzle. The control valve and the pressure gauge are available in this system. The pressure of the colour paint can be controlled by using control valve. The nozzle is used to spray the colour paint evenly to the rollers for impression the desired matter on the polymer rolls. If the product changes, the operator do not need take excess time for cleaning and altering the paint just removing the existing reservoir to place the new one.

ZERO SETTING ADJUSTMENT

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The stereos are pasted on the cylinder approximately and the operator is to adjust the cylinder to align it in accurately. The worker need trail time for checking whether the alignment of cylinder is right or wrong. This leads to a non value added time. The total time taken for cylinder alignment is about 19.30 minutes including trail time. To avoid this waste, zero setting adjustment technique can be used and it is shown in the figure. The punch number is used to mark in the cylinder for various products and these marks are to identifying for pasting the master sheet of particular product. Now paste the stereo in the master sheet and it is to glue in the specified mark of cylinder. This minimizes the trail time and errors. After implementing vacuum pump system and zero setting adjustment the setup time can be minimized and it is listed in the below table.

 S. no.                     Task operation        Target time
 

1.

 

Stereo pasting

 

1.30 min

 

2.

 

Colour changing

 

3.00 min

 

3.

 

Cylinder alignment

 

3.00 min

 

4.

 

Trail time

 

 

5.

 

Regular process starts

 

7.30 min

The above table shows clearly about the working time period in minutes. The company is running only one shift and is about 420 minutes except of break time. The setup time takes 34.30 minutes then the total time for running roll printing machine is 385.30 minutes and this is a regular procedure which the company follows. After implementing SMED, the changeover time is reduced to 7.30 minutes and running time is 412.30 minutes. The following chart shows the time comparison between the before & after implementation of SMED.

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The above chart shows the relationship time between the before and after implementation of “Vacuum pump system” and “Zero setting adjustment” in the roll printing machine. It also illustrates the minimized non value added time.

BASIC CALCULATIONS AND TABULATIONS

  • Total no. of shifts = 1
  • 1 shift = 8 hours
  • Break time = 1 hour
  • Total working time = 8-1 = 7 hours = 420 minutes
  • of meters produced per hour = 2000 m
  • of meters produced per minute = 33.33 meters
  • No of working days per year = 313 days
 

 

Process

Working time      per

shift (min)

Number of meters produced per

 Minute

Total number of meters produced per

day

Total number of meters produced

 per

month

Total

 number of meters produced

per

year

 

Current state

 

 

385.30

 

 

33.33

 

12,842.049

 

 

3,33,893.274

 

 

40,19,561.337

 

Future state

 

 

412.30

 

 

33.33

 

13,741.959

 

 

3,57,290.934

 

 

43,01,233.167

CONCLUSION

The lean technique, SMED was implemented and significant result was achieved. Based on a series of time study data collected during the setup activities in the roll printing machine, a comparison of results and achievements before and after the SMED implementation was made to measure the effectiveness of SMED to reduce setup time. The goal is to reduce the non value added time and reduction in setup time makes it possible to increase manufacturing system flexibility to manufacture a variety of products. By implementing the SMED techniques, the total time taken to perform setup activities at roll printing machine was reduced by from 34.30 minutes to 7.30 minutes i.e. 27 minutes reduced and production rate has been increased from 40,19,561.337 meters to 43,01,233.167 meters i.e. 2,81,671.83 meters increased. This in turn reduces costs and increase in productivity.




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